The invention applies more particularly to systems giving “hands free” access to and/or starting of motor vehicles. A so-called “hands free” system for access to a motor vehicle makes it possible for an authorized user to lock and/or unlock the openings of his vehicle and/or to start the vehicle without using a key. In order to do this, the vehicle proceeds with the identification of a portable device such as a badge or a remote control carried by the user and if the badge or the remote control is situated in a predetermined zone around the vehicle and is identified as belonging to the vehicle, then the vehicle automatically locks/unlocks its openings or starts according to the user's intention, without the user having to use a key.
This “hands free” access system is known to those skilled in the art. It is generally composed of an electronic control unit installed in the vehicle, one or more radiofrequency (RF) antennas situated on the vehicle and an identification badge or remote control comprising an RF antenna carried by the user.
An identifier exchange between the portable device and the vehicle by the intermediary of the RF antennas and the electronic control unit allows the identification of the portable device by the vehicle and the triggering of the locking or unlocking of the openings or the starting by the latter.
The identifier can be contained in a portable device other than a badge or a remote control, for example it can be contained in a mobile telephone or “smartphone” in English (“telephone intelligent” in French), or in a watch worn by the user.
The identifier exchange is generally carried out by Radio Frequency (RF) waves and by Low Frequency (or LF, standing for “Low frequency” in English) waves. The vehicle firstly transmits, by the intermediary of the LF antennas, an LF interrogation signal and the portable device, if it is situated in the reception zone of the said signal (i.e. a predetermined zone around the vehicle), returns an RF presence message to the vehicle containing its identifier.
The precise location of the portable device around the vehicle is carried out by a measurement of the strength of the LF signal received by the portable device (via the antennas and the electronic control unit) coming from the vehicle, more commonly called RSSI (“Received Signal Strength Indication” in English, or measurement of the received power of a signal received by an antenna) measurements. The measurement of the strength of the signal received by the portable device coming from each LF antenna, is received and analyzed by a location device installed in the vehicle, which thus determines the position of the portable device with respect to the said LF antennas, that is to say with respect to the vehicle.
The location device D generally comprises the electronic control unit 10 and three to four antennas A1, A2, A3, A4 and is shown in FIG. 1.
FIG. 1 shows three location zones of the portable device P around the vehicle V, a first zone Z1 covering the interior of the passenger compartment of the vehicle, a second zone Z2 covering the first zone Z1 and a zone which is external but close to the vehicle, and a third zone Z3, covering the first and second zones Z1, Z2 and an enlarged external zone around the vehicle V.
According to the location of the portable device P identified by the vehicle, in the said location zones Z1, Z2, Z3, certain actions specific to the said location zones are carried out automatically: starting the vehicle, unlocking/locking or prior switching on the passenger compartment lighting (also called “welcome lighting” in English).
The RSSI measurement makes it possible to locate precisely the portable device P in the location zones, that is to say around and inside the vehicle V in order to allow not only the locking/unlocking of the openings but also the starting of the vehicle V, when the portable device P is detected in the interior of the vehicle V.
In the case where the portable device is a mobile telephone, the communication with the vehicle in RF (for example in the ISM bands) and LF (for example at 125 kHz) is not always possible, because most mobile telephones do not have RF or LF communication means whose frequencies are compatible with those used during the communication with a vehicle, such as the frequencies of 315 MHz and 433.92 MHz for the RF and 125 kHz for the LF.
On the other hand, as of this moment, mobile telephones have the Bluetooth® or Bluetooth Low Energy (BLE) communication standard, that is to say communication at Ultra High Frequency (UHF) from 2400 MHz to 2480 MHz. This communication standard has the advantage of being universal and therefore does not necessitate approval specific to each country (only an international “Bluetooth Low Energy” certification), as is the case with the current RF and LF communication standards whose operating frequencies differ depending on the country.
It therefore becomes necessary to adapt the “hands free” vehicle access and/or starting system so that it can also operate with a mobile telephone equipped with the Bluetooth® communication standard and no longer solely by the intermediary of radio and low frequency (RF, LF) waves.
The advantage of the Bluetooth® communication standard is that it allows a long communication range of about 250 m around the vehicle. However, it does not make it possible to detect precisely the presence of the portable device at shorter distances. For example, when the portable device P is about ten centimeters from the vehicle V and the user wishes to unlock his vehicle, the precise location of the portable device which was possible with the communication device of the prior art, operating with an exchange by RF and LF waves, is no longer possible by Bluetooth®. In fact, the RSSI measurement of a Bluetooth signal is very imprecise and varies enormously as a function of the environment (noise, interference) and it is not possible to know if the portable device, whose position is fixed, is 5 m or 10 m or 40 m or more from the vehicle.
It is therefore no longer possible to start the vehicle by using Bluetooth®, communication since the starting must be authorized only when the portable device is inside of the vehicle and a few centimeters from the UHF antennas of the vehicle. Given the great variation of the RSSI of Bluetooth®, the detection of the said portable device a few centimeters from the UHF antennas is not possible.
Now, Bluetooth® communication is a communication protocol which is optimized with respect to interference, since it is carried out sequentially on several different frequency channels (also called “multi-channel” communication), generally on three channels, in order to be as little sensitive as possible to external interference, for example to interference coming from a Wifi™ communication (wireless communication).
Bluetooth® communication in fact consists of the successive transmission of data on three separate frequency channels, for example: 2.402 GHz, then 2.426 GHz, and finally on 2.480 GHz. By multiplying the transmission channels, the probability of interference on the three frequencies at the same time is low, and the communication with the portable device is therefore ensured at least on one frequency. However, the precise location of the said portable device remains impossible.
The invention proposes a device for the ultra high frequency location of the portable device making it possible to overcome these disadvantages.
In this case, the invention proposes a method using ultra high frequency waves for locating a portable device for giving “hands free” access to and/or starting of a motor vehicle making it possible to locate precisely the portable device inside and outside of the vehicle, in order to be able to initiate appropriate actions such as for example the automatic unlocking/locking of the doors and the starting of the vehicle.